Method for operating a fast random access procedure in a wireless communication system and a device therefor

ABSTRACT

The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for operating fast random access procedure in a wireless communication system, the method comprising: transmitting a RAP including a first RAP ID to an e-NodeB; starting monitoring a Physical Downlink Control Channel PDCCH addressed by RA-RNTI during RAR window; receiving, from the eNB, an indicator including at least one RAP ID, wherein one of the at least one RAP ID matches to the first RAP ID; and stopping monitoring the PDCCH addressed by RA-RNTI upon reception of the indicator.

This application claims the benefit of 35 U.S.C. § 371 National StageEntry of International Application No. PCT/KR2016/002294 filed on Mar.8, 2016 and claims the benefit of U.S. Provisional Application No.62/130,537 filed on Mar. 9, 2015, all of which are incorporated byreference in their entirety herein.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method for operating a fast random accessprocedure in a wireless communication system and a device therefor.

BACKGROUND ART

As an example of a mobile communication system to which the presentinvention is applicable, a 3rd Generation Partnership Project Long TermEvolution (hereinafter, referred to as LTE) communication system isdescribed in brief.

FIG. 1 is a view schematically illustrating a network structure of anE-UMTS as an exemplary radio communication system. An Evolved UniversalMobile Telecommunications System (E-UMTS) is an advanced version of aconventional Universal Mobile Telecommunications System (UMTS) and basicstandardization thereof is currently underway in the 3GPP. E-UMTS may begenerally referred to as a Long Term Evolution (LTE) system. For detailsof the technical specifications of the UMTS and E-UMTS, reference can bemade to Release 7 and Release 8 of “3rd Generation Partnership Project;Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs(eNBs), and an Access Gateway (AG) which is located at an end of thenetwork (E-UTRAN) and connected to an external network. The eNBs maysimultaneously transmit multiple data streams for a broadcast service, amulticast service, and/or a unicast service.

One or more cells may exist per eNB. The cell is set to operate in oneof bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides adownlink (DL) or uplink (UL) transmission service to a plurality of UEsin the bandwidth. Different cells may be set to provide differentbandwidths. The eNB controls data transmission or reception to and froma plurality of UEs. The eNB transmits DL scheduling information of DLdata to a corresponding UE so as to inform the UE of a time/frequencydomain in which the DL data is supposed to be transmitted, coding, adata size, and hybrid automatic repeat and request (HARQ)-relatedinformation. In addition, the eNB transmits UL scheduling information ofUL data to a corresponding UE so as to inform the UE of a time/frequencydomain which may be used by the UE, coding, a data size, andHARQ-related information. An interface for transmitting user traffic orcontrol traffic may be used between eNBs. A core network (CN) mayinclude the AG and a network node or the like for user registration ofUEs. The AG manages the mobility of a UE on a tracking area (TA) basis.One TA includes a plurality of cells.

Although wireless communication technology has been developed to LTEbased on wideband code division multiple access (WCDMA), the demands andexpectations of users and service providers are on the rise. Inaddition, considering other radio access technologies under development,new technological evolution is required to secure high competitivenessin the future. Decrease in cost per bit, increase in serviceavailability, flexible use of frequency bands, a simplified structure,an open interface, appropriate power consumption of UEs, and the likeare required.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ina method and device for operating a fast random access procedure in awireless communication system. The technical problems solved by thepresent invention are not limited to the above technical problems andthose skilled in the art may understand other technical problems fromthe following description.

Technical Solution

The object of the present invention can be achieved by providing amethod for User Equipment (UE) operating in a wireless communicationsystem as set forth in the appended claims.

In another aspect of the present invention, provided herein is acommunication apparatus as set forth in the appended claims.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

Advantageous Effects

According to the present invention, operating a fast random accessprocedure can be useful for latency reduction or power saving.Specifically, when the eNB transmits an indicator which indicates theRAP that the eNB has not successfully decoded or received, the UEconsiders the RAR reception not successful and proceeds to the selectionof a random access resource although the RAR window is not ended.

It will be appreciated by persons skilled in the art that the effectsachieved by the present invention are not limited to what has beenparticularly described hereinabove and other advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention.

FIG. 1 is a diagram showing a network structure of an Evolved UniversalMobile Telecommunications System (E-UMTS) as an example of a wirelesscommunication system;

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS), and FIG. 2B is ablock diagram depicting architecture of a typical E-UTRAN and a typicalEPC;

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3rd generationpartnership project (3GPP) radio access network standard;

FIG. 4 is a view showing an example of a physical channel structure usedin an E-UMTS system;

FIG. 5 is a block diagram of a communication apparatus according to anembodiment of the present invention;

FIG. 6 is a diagram for an example method for performing anon-contention-based random access procedure;

FIG. 7 is a diagram for an example method for performing acontention-based random access procedure;

FIG. 8 is a view illustrating for interaction model between L1 and L2/3for Random Access Procedure;

FIGS. 9A to 9D are diagrams for MAC PDU including Random AccessResponse;

FIGS. 10 and 11 are conceptual diagrams for operating fast random accessprocedure in a wireless communication system according to embodiments ofthe present invention;

FIG. 12 is an example scenario for operating fast random accessprocedure in a wireless communication system according to embodiments ofthe present invention; and

FIGS. 13A to 13D are diagrams for a new MAC PDU according to embodimentsof the present invention.

BEST MODE

Universal mobile telecommunications system (UMTS) is a 3rd Generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). The long-term evolution (LTE) of UMTS is under discussion by the3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3G LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

Hereinafter, structures, operations, and other features of the presentinvention will be readily understood from the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Embodiments described later are examples in which technicalfeatures of the present invention are applied to a 3GPP system.

Although the embodiments of the present invention are described using along term evolution (LTE) system and a LTE-advanced (LTE-A) system inthe present specification, they are purely exemplary. Therefore, theembodiments of the present invention are applicable to any othercommunication system corresponding to the above definition. In addition,although the embodiments of the present invention are described based ona frequency division duplex (FDD) scheme in the present specification,the embodiments of the present invention may be easily modified andapplied to a half-duplex FDD (H-FDD) scheme or a time division duplex(TDD) scheme.

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS). The E-UMTS may bealso referred to as an LTE system. The communication network is widelydeployed to provide a variety of communication services such as voice(VoIP) through IMS and packet data.

As illustrated in FIG. 2A, the E-UMTS network includes an evolved UMTSterrestrial radio access network (E-UTRAN), an Evolved Packet Core (EPC)and one or more user equipment. The E-UTRAN may include one or moreevolved NodeB (eNodeB) 20, and a plurality of user equipment (UE) 10 maybe located in one cell. One or more E-UTRAN mobility management entity(MME)/system architecture evolution (SAE) gateways 30 may be positionedat the end of the network and connected to an external network.

As used herein, “downlink” refers to communication from eNodeB 20 to UE10, and “uplink” refers to communication from the UE to an eNodeB. UE 10refers to communication equipment carried by a user and may be alsoreferred to as a mobile station (MS), a user terminal (UT), a subscriberstation (SS) or a wireless device.

FIG. 2B is a block diagram depicting architecture of a typical E-UTRANand a typical EPC.

As illustrated in FIG. 2B, an eNodeB 20 provides end points of a userplane and a control plane to the UE 10. MME/SAE gateway 30 provides anend point of a session and mobility management function for UE 10. TheeNodeB and MME/SAE gateway may be connected via an S1 interface.

The eNodeB 20 is generally a fixed station that communicates with a UE10, and may also be referred to as a base station (BS) or an accesspoint. One eNodeB 20 may be deployed per cell. An interface fortransmitting user traffic or control traffic may be used between eNodeBs20.

The MME provides various functions including NAS signaling to eNodeBs20, NAS signaling security, AS Security control, Inter CN node signalingfor mobility between 3GPP access networks, Idle mode UE Reachability(including control and execution of paging retransmission), TrackingArea list management (for UE in idle and active mode), PDN GW andServing GW selection, MME selection for handovers with MME change, SGSNselection for handovers to 2G or 3G 3GPP access networks, Roaming,Authentication, Bearer management functions including dedicated bearerestablishment, Support for PWS (which includes ETWS and CMAS) messagetransmission. The SAE gateway host provides assorted functions includingPer-user based packet filtering (by e.g. deep packet inspection), LawfulInterception, UE IP address allocation, Transport level packet markingin the downlink, UL and DL service level charging, gating and rateenforcement, DL rate enforcement based on APN-AMBR. For clarity MME/SAEgateway 30 will be referred to herein simply as a “gateway,” but it isunderstood that this entity includes both an MME and an SAE gateway.

A plurality of nodes may be connected between eNodeB 20 and gateway 30via the S1 interface. The eNodeBs 20 may be connected to each other viaan X2 interface and neighboring eNodeBs may have a meshed networkstructure that has the X2 interface.

As illustrated, eNodeB 20 may perform functions of selection for gateway30, routing toward the gateway during a Radio Resource Control (RRC)activation, scheduling and transmitting of paging messages, schedulingand transmitting of Broadcast Channel (BCCH) information, dynamicallocation of resources to UEs 10 in both uplink and downlink,configuration and provisioning of eNodeB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE-IDLE state management,ciphering of the user plane, System Architecture Evolution (SAE) bearercontrol, and ciphering and integrity protection of Non-Access Stratum(NAS) signaling.

The EPC includes a mobility management entity (MME), a serving-gateway(S-GW), and a packet data network-gateway (PDN-GW). The MME hasinformation about connections and capabilities of UEs, mainly for use inmanaging the mobility of the UEs. The S-GW is a gateway having theE-UTRAN as an end point, and the PDN-GW is a gateway having a packetdata network (PDN) as an end point.

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3GPP radioaccess network standard. The control plane refers to a path used fortransmitting control messages used for managing a call between the UEand the E-UTRAN. The user plane refers to a path used for transmittingdata generated in an application layer, e.g., voice data or Internetpacket data.

A physical (PHY) layer of a first layer provides an information transferservice to a higher layer using a physical channel. The PHY layer isconnected to a medium access control (MAC) layer located on the higherlayer via a transport channel. Data is transported between the MAC layerand the PHY layer via the transport channel Data is transported betweena physical layer of a transmitting side and a physical layer of areceiving side via physical channels. The physical channels use time andfrequency as radio resources. In detail, the physical channel ismodulated using an orthogonal frequency division multiple access (OFDMA)scheme in downlink and is modulated using a single carrier frequencydivision multiple access (SC-FDMA) scheme in uplink.

The MAC layer of a second layer provides a service to a radio linkcontrol (RLC) layer of a higher layer via a logical channel. The RLClayer of the second layer supports reliable data transmission. Afunction of the RLC layer may be implemented by a functional block ofthe MAC layer. A packet data convergence protocol (PDCP) layer of thesecond layer performs a header compression function to reduceunnecessary control information for efficient transmission of anInternet protocol (IP) packet such as an IP version 4 (IPv4) packet oran IP version 6 (IPv6) packet in a radio interface having a relativelysmall bandwidth.

A radio resource control (RRC) layer located at the bottom of a thirdlayer is defined only in the control plane. The RRC layer controlslogical channels, transport channels, and physical channels in relationto configuration, re-configuration, and release of radio bearers (RBs).An RB refers to a service that the second layer provides for datatransmission between the UE and the E-UTRAN. To this end, the RRC layerof the UE and the RRC layer of the E-UTRAN exchange RRC messages witheach other.

One cell of the eNB is set to operate in one of bandwidths such as 1.25,2.5, 5, 10, 15, and 20 MHz and provides a downlink or uplinktransmission service to a plurality of UEs in the bandwidth. Differentcells may be set to provide different bandwidths.

Downlink transport channels for transmission of data from the E-UTRAN tothe UE include a broadcast channel (BCH) for transmission of systeminformation, a paging channel (PCH) for transmission of paging messages,and a downlink shared channel (SCH) for transmission of user traffic orcontrol messages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted through the downlink SCH and mayalso be transmitted through a separate downlink multicast channel (MCH).

Uplink transport channels for transmission of data from the UE to theE-UTRAN include a random access channel (RACH) for transmission ofinitial control messages and an uplink SCH for transmission of usertraffic or control messages. Logical channels that are defined above thetransport channels and mapped to the transport channels include abroadcast control channel (BCCH), a paging control channel (PCCH), acommon control channel (CCCH), a multicast control channel (MCCH), and amulticast traffic channel (MTCH).

FIG. 4 is a view showing an example of a physical channel structure usedin an E-UMTS system. A physical channel includes several subframes on atime axis and several subcarriers on a frequency axis. Here, onesubframe includes a plurality of symbols on the time axis. One subframeincludes a plurality of resource blocks and one resource block includesa plurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use certain subcarriers of certain symbols (e.g., a firstsymbol) of a subframe for a physical downlink control channel (PDCCH),that is, an L1/L2 control channel. In FIG. 4, an L1/L2 controlinformation transmission area (PDCCH) and a data area (PDSCH) are shown.In one embodiment, a radio frame of 10 ms is used and one radio frameincludes 10 subframes. In addition, one subframe includes twoconsecutive slots. The length of one slot may be 0.5 ms. In addition,one subframe includes a plurality of OFDM symbols and a portion (e.g., afirst symbol) of the plurality of OFDM symbols may be used fortransmitting the L1/L2 control information. A transmission time interval(TTI) which is a unit time for transmitting data is 1 ms.

A base station and a UE mostly transmit/receive data via a PDSCH, whichis a physical channel, using a DL-SCH which is a transmission channel,except a certain control signal or certain service data. Informationindicating to which UE (one or a plurality of UEs) PDSCH data istransmitted and how the UE receive and decode PDSCH data is transmittedin a state of being included in the PDCCH.

For example, in one embodiment, a certain PDCCH is CRC-masked with aradio network temporary identity (RNTI) “A” and information about datais transmitted using a radio resource “B” (e.g., a frequency location)and transmission format information “C” (e.g., a transmission blocksize, modulation, coding information or the like) via a certainsubframe. Then, one or more UEs located in a cell monitor the PDCCHusing its RNTI information. And, a specific UE with RNTI “A” reads thePDCCH and then receive the PDSCH indicated by B and C in the PDCCHinformation.

FIG. 5 is a block diagram of a communication apparatus according to anembodiment of the present invention.

The apparatus shown in FIG. 5 can be a user equipment (UE) and/or eNBadapted to perform the above mechanism, but it can be any apparatus forperforming the same operation.

As shown in FIG. 5, the apparatus may comprise a DSP/microprocessor(110) and RF module (transceiver; 135). The DSP/microprocessor (110) iselectrically connected with the transceiver (135) and controls it. Theapparatus may further include power management module (105), battery(155), display (115), keypad (120), SIM card (125), memory device (130),speaker (145) and input device (150), based on its implementation anddesigner's choice.

Specifically, FIG. 5 may represent a UE comprising a receiver (135)configured to receive a request message from a network, and atransmitter (135) configured to transmit the transmission or receptiontiming information to the network. These receiver and transmitter canconstitute the transceiver (135). The UE further comprises a processor(110) connected to the transceiver (135: receiver and transmitter).

Also, FIG. 5 may represent a network apparatus comprising a transmitter(135) configured to transmit a request message to a UE and a receiver(135) configured to receive the transmission or reception timinginformation from the UE. These transmitter and receiver may constitutethe transceiver (135). The network further comprises a processor (110)connected to the transmitter and the receiver. This processor (110) maybe configured to calculate latency based on the transmission orreception timing information.

Recently, Proximity-based Service (ProSe) has been discussed in 3GPP.The ProSe enables different UEs to be connected (directly) each other(after appropriate procedure(s), such as authentication), through eNBonly (but not further through Serving Gateway (SGW)/Packet Data NetworkGateway (PDN-GW, PGW)), or through SGW/PGW. Thus, using the ProSe,device to device direct communication can be provided, and it isexpected that every devices will be connected with ubiquitousconnectivity. Direct communication between devices in a near distancecan lessen the load of network. Recently, proximity-based social networkservices have come to public attention, and new kinds of proximity-basedapplications can be emerged and may create new business market andrevenue. For the first step, public safety and critical communicationare required in the market. Group communication is also one of keycomponents in the public safety system. Required functionalities are:Discovery based on proximity, Direct path communication, and Managementof group communications.

Use cases and scenarios are for example: i) Commercial/social use, ii)Network offloading, iii) Public Safety, iv) Integration of currentinfrastructure services, to assure the consistency of the userexperience including reachability and mobility aspects, and v) PublicSafety, in case of absence of EUTRAN coverage (subject to regionalregulation and operator policy, and limited to specific public-safetydesignated frequency bands and terminals).

Similarly, Machine Type Communication (MTC) refers to a communicationscheme between one or more machines and is also referred to asmachine-to-machine (M2M) communication. Here, a machine refers to anentity which does not require direct human operation or intervention.For example, examples of the machine may include not only a deviceincluding a mobile communication module, such as a meter or a vendingmachine, but also a user equipment such as a smartphone which is capableof automatically accessing a network without operation/intervention of auser to perform communication. Various examples of such a machine arereferred to as an MTC device or terminal in the present specification.That is, MTC refers to communication performed by one or more machines(that is, MTC devices) without human operation/intervention.

MTC may include communication between MTC devices and communicationbetween an MTC device and an MTC application server. Examples ofcommunication between an MTC device and an MTC application serverinclude communication between a vending machine and a server,communication between a point of sale (POS) device and a server and anelectric meter, and communication between a gas meter or a water meterand a server. MTC-based applications may include security,transportation, healthcare, etc.

In case of Machine Type Communication using the M2M devices, or ProSecommunication using the D2D devices, power saving or latency reductionis one of important issues in this technology. Thus, to achieve thepower saving or latency reduction, conventional Random Access procedurecan be changed appropriately.

FIGS. 6 and 7 are views illustrating an operating procedure of aterminal (UE) and a base station (eNB) in random access procedure. FIG.6 is corresponding to non-contention based random access procedure andFIG. 7 is corresponding to contention based random access procedure.

The random access procedure takes two distinct forms. One is acontention based (applicable to first five events) random accessprocedure and the other one is a non-contention based (applicable toonly handover, DL data arrival and positioning) random access procedure.The non-contention based random access procedure is also called asdedicated RACH process.

The random access procedure is performed for the following eventsrelated to the PCell: i) initial access from RRC_IDLE; ii) RRCConnection Re-establishment procedure; iii) Handover; iv) DL dataarrival during RRC_CONNECTED requiring random access procedure (e.g.when UL synchronization status is “non-synchronized”.), v) UL dataarrival during RRC_CONNECTED requiring random access procedure (e.g.when UL synchronization status is “non-synchronized” or there are noPUCCH resources for SR available), and vi) For positioning purposeduring RRC_CONNECTED requiring random access procedure; (e.g. whentiming advance is needed for UE positioning.)

The random access procedure is also performed on a SCell to establishtime alignment for the corresponding sTAG. In DC, the random accessprocedure is also performed on at least PSCell upon SCGaddition/modification, if instructed, or upon DL/UL data arrival duringRRC_CONNECTED requiring random access procedure. The UE initiated randomaccess procedure is performed only on PSCell for SCG.

Regarding FIG. 6, FIG. 6 shows the non-contention based random accessprocedure. As described above, a non-contention based random accessprocedure may be performed in a handover procedure and when the randomaccess procedure is requested by a command of an eNode B. Even in thesecases, a contention based random access procedure may be performed.

First, it is important that a specific random access preamble withoutthe possibility of collision is received from the eNode B, for thenon-contention based random access procedure.

The UE receives an assigned random access preamble (S601). Methods ofreceiving the random access preamble may include a method using HOcommand generated by target eNB and sent via source eNB for handover, amethod using a Physical Downlink Control Channel (PDCCH) in case of DLdata arrival or positioning, and PDCCH for initial UL time alignment fora sTAG.

The UE transmits the preamble to the eNode B after receiving theassigned random access preamble from the eNode B as described above(S603).

The UE attempts to receive a random access response within a randomaccess response reception window indicated by the eNode B throughhandover command or system information after transmitting the randomaccess preamble in step S603 (S605). More specifically, the randomaccess response information may be transmitted in the form of a MediumAccess Control (MAC) Packet Data Unit (PDU), and the MAC PDU may betransferred via a Physical Downlink Shared Channel (PDSCH). In addition,the UE preferably monitors the PDCCH in order to enable to the UE toproperly receive the information transferred via the PDSCH. That is, thePDCCH may preferably include information about a UE that should receivethe PDSCH, frequency and time information of radio resources of thePDSCH, a transfer format of the PDSCH, and the like. Here, if the PDCCHhas been successfully received, the UE may appropriately receive therandom access response transmitted on the PDSCH according to informationof the PDCCH. The random access response may include a random accesspreamble identifier (e.g. Random Access-Radio Network TemporaryIdentifier (RA-RNTI)), an UL Grant indicating uplink radio resources, atemporary C-RNTI, a Time Advance Command (TAC), and the like.

As described above, the reason why the random access response includesthe random access preamble identifier is because a single random accessresponse may include random access response information of at least oneUE and thus it is reported to which UE the UL Grant, the TemporaryC-RNTI and the TAC are valid. In this step, it is assumed that the UEselects a random access preamble identifier matched to the random accesspreamble selected by the UE in step S603.

In the non-contention based random access procedure, it is determinedthat the random access procedure is normally performed, by receiving therandom access response information, and the random access procedure maybe finished.

FIG. 7 is a view illustrating an operating procedure of a UE and an eNBin a contention based random access procedure.

First, the UE may randomly select a single random access preamble from aset of random access preambles indicated through system information or ahandover command, and select and transmit a Physical Random AccessChannel (PRACH) capable of transmitting the random access preamble(S701).

There are two possible groups defined and one is optional. If bothgroups are configured the size of message 3 and the pathloss are used todetermine which group a preamble is selected from. The group to which apreamble belongs provides an indication of the size of the message 3 andthe radio conditions at the UE. The preamble group information alongwith the necessary thresholds is broadcast on system information.

A method of receiving random access response information is similar tothe above-described non-contention based random access procedure. Thatis, the UE attempts to receive its own random access response within arandom access response reception window indicated by the eNode B throughthe system information or the handover command, after the random accesspreamble is transmitted in step S701, and receives a Physical DownlinkShared Channel (PDSCH) using random access identifier informationcorresponding thereto (S703). Accordingly, the UE may receive a ULGrant, a Temporary C-RNTI, a TAC and the like.

If the UE has received the random access response valid for the UE, theUE may process all of the information included in the random accessresponse. That is, the UE applies the TAC, and stores the temporaryC-RNTI. In addition, data which will be transmitted in correspondencewith the reception of the valid random access response may be stored inan Msg3 buffer.

The UE uses the received UL Grant so as to transmit the data (that is,the message 3) to the eNode B (S705). The message 3 should include a UEidentifier. In the contention based random access procedure, the eNode Bmay not determine which UEs are performing the random access procedure,but later the UEs should be identified for contention resolution.

Here, two different schemes for including the UE identifier may beprovided. A first scheme is to transmit the UE's cell identifier throughan uplink transmission signal corresponding to the UL Grant if the UEhas already received a valid cell identifier allocated by acorresponding cell prior to the random access procedure. Conversely, thesecond scheme is to transmit the UE's unique identifier (e.g., S-TMSI orrandom ID) if the UE has not received a valid cell identifier prior tothe random access procedure. In general, the unique identifier is longerthan the cell identifier. If the UE has transmitted data correspondingto the UL Grant, the UE starts a contention resolution (CR) timer.

After transmitting the data with its identifier through the UL Grantincluded in the random access response, the UE waits for an indication(instruction) from the eNode B for contention resolution. That is, theUE attempts to receive the PDCCH so as to receive a specific message(S707). Here, there are two schemes to receive the PDCCH. As describedabove, the UE attempts to receive the PDCCH using its own cellidentifier if the message 3 transmitted in correspondence with the ULGrant is transmitted using the UE's cell identifier, and the UE attemptsto receive the PDCCH using the temporary C-RNTI included in the randomaccess response if the identifier is its unique identifier. Thereafter,in the former scheme, if the PDCCH is received through its own cellidentifier before the contention resolution timer is expired, the UEdetermines that the random access procedure has been normally performedand completes the random access procedure. In the latter scheme, if thePDCCH is received through the temporary C-RNTI before the contentionresolution timer has expired, the UE checks data transferred by thePDSCH indicated by the PDCCH. If the unique identifier of the UE isincluded in the data, the UE determines that the random access procedurehas been normally performed and completes the random access procedure.

The Temporary C-RNTI is promoted to C-RNTI for a UE which detects RAsuccess and does not already have a C-RNTI; it is dropped by others. AUE which detects RA success and already has a C-RNTI, resumes using itsC-RNTI.

In the step of S703, Random Access Response reception is started afterthe UE transmits a Random Access Preamble. Once the Random AccessPreamble is transmitted and regardless of the possible occurrence of ameasurement gap, the MAC entity shall monitor the PDCCH of the SpCellfor Random Access Response(s) identified by the RA-RNTI defined below,in the RA Response window which starts at the subframe that contains theend of the preamble transmission plus three subframes and has lengthra-ResponseWindowSize subframes.

The RA-RNTI associated with the PRACH in which the Random AccessPreamble is transmitted, is computed as:RA-RNTI=1+t_id+10*f_id

Where t_id is the index of the first subframe of the specified PRACH(0≤t_id<10), and f_id is the index of the specified PRACH within thatsubframe, in ascending order of frequency domain (0≤f_id<6).

The MAC entity may stop monitoring for Random Access Response(s) aftersuccessful reception of a Random Access Response containing RandomAccess Preamble identifiers that matches the transmitted Random AccessPreamble.

If no Random Access Response is received within the RA Response window,or if none of all received Random Access Responses contains a RandomAccess Preamble identifier corresponding to the transmitted RandomAccess Preamble, the Random Access Response reception is considered notsuccessful.

When the Random Access Response reception is considered not successful,the MAC entity increments PREAMBLE_TRANSMISSION_COUNTER by 1 if thenotification of power ramping suspension has not been received fromlower layers.

If in this Random Access procedure, the Random Access Preamble wasselected by MAC, the MAC entity selects a random backoff time accordingto a uniform distribution between 0 and the Backoff Parameter Valuebased on the backoff parameter, and delays the subsequent Random Accesstransmission by the backoff time. And the MAC entity proceeds toselection of a Random Access Resource. The Random Access Resourceselection includes the following performance: i) selection of RandomAccess Preamble, ii) determination of the next available subframecontaining PRACH, or iii) transmission of Random Access Preamble.

FIG. 8 is a view illustrating for interaction model between L1 and L2/3for Random Access Procedure.

Random access procedure described above is modelled in FIG. 8 below fromL1 and L2/3 interaction point of view. L2/L3 receives indication from L1whether ACK is received or DTX is detected after indication of RandomAccess Preamble transmission to L1. L2/3 indicates L1 to transmit firstscheduled UL transmission (RRC Connection Request in case of initialaccess) if necessary or Random Access Preamble based on the indicationfrom L1.

FIGS. 9A to 9D are diagrams for MAC PDU including Random AccessResponse.

FIG. 9A is an example of MAC PDU consisting of a MAC header and MACRARs. A MAC PDU consists of a MAC header and zero or more MAC RandomAccess Responses (MAC RAR) and optionally padding.

The MAC header is of variable size. A MAC PDU header consists of one ormore MAC PDU subheaders; each subheader corresponding to a MAC RARexcept for the Backoff Indicator subheader. If included, the BackoffIndicator subheader is only included once and is the first subheaderincluded within the MAC PDU header.

A MAC PDU subheader consists of the three header fields E/T/RAPID (asdescribed in FIG. 9B) but for the Backoff Indicator subheader whichconsists of the five header field E/T/R/R/BI (as described in FIG. 9C).

A MAC RAR consists of the four fields R/Timing Advance Command/ULGrant/Temporary C-RNTI (as described in FIG. 9D). Padding may occurafter the last MAC RAR. Presence and length of padding is implicit basedon TB size, size of MAC header and number of RARs.

The MAC header is of variable size and consists of the following fields:

-   -   E: The Extension field is a flag indicating if more fields are        present in the MAC header or not. The E field is set to “1” to        indicate at least another set of E/T/RAPID fields follows. The E        field is set to “0” to indicate that a MAC RAR or padding starts        at the next byte;    -   T: The Type field is a flag indicating whether the MAC subheader        contains a Random Access ID or a Backoff Indicator. The T field        is set to “0” to indicate the presence of a Backoff Indicator        field in the subheader (BI). The T field is set to “1” to        indicate the presence of a Random Access Preamble ID field in        the subheader (RAPID);    -   R: Reserved bit, set to “0”;    -   BI: The Backoff Indicator field identifies the overload        condition in the cell. The size of the BI field is 4 bits;    -   RAPID: The Random Access Preamble IDentitfier field identifies        the transmitted Random Access Preamble. The size of the RAPID        field is 6 bits.

The MAC header and subheaders are octet aligned.

For random access (RA) procedure, the UE transmits a random accesspreamble (RAP) to the eNB and then the UE shall monitor the PDCCHaddressed by RA-RNTI during Random Access Response (RAR) window. RARwindow starts at the subframe that contains the end of the RAPtransmission plus three subframes and has length ra-ResponseWindowSizesubframes.

During the RAR window, the UE shall monitor the PDCCH in order toreceive RAR which contains the RAP ID that the UE transmitted to theeNB. After successful reception of a RAR containing the transmitted RAP,the UE may stop monitoring the PDCCH addressed by RA-RNTI.

This implies that if the UE has not received a RAR containing the RAP IDcorresponding to the transmitted RAP, the UE shall continue monitoringthe PDCCH during RAR window because the eNB may transmit the RARcontaining the transmitted RAP ID at any point in time during RARwindow. However, in case the eNB has not successfully decoded orreceived the RAP that the UE transmitted, the UE will eventually cannotreceive a RAR containing the transmitted RAP ID. This brings unnecessarymonitoring of PDCCH from the UE point of view and delays additionaltransmission of RAP and whole RA procedure accordingly.

Currently, there is no method for a UE to predict that the eNB will nottransmit the RAR containing the transmitted RAP ID during RAR window sothat the UE is not going to receive the RAR containing the transmittedRAP ID during RAR window. If the UE can predict whether the UE wouldreceive RAR containing the transmitted RAP ID or not during RAR window,the UE can perform RA procedure in a faster and more efficient manner.

FIG. 10 is a conceptual diagram for operating fast random accessprocedure in a wireless communication system according to embodiments ofthe present invention.

In this invention, after a UE transmits a random access preamble (RAP),it is proposed that the UE stops monitoring PDCCH addressed by RA-RNTIduring Random Access Response (RAR) window if the UE receives anindicator from the eNB which indicates that the transmitted RAP was notsuccessfully decoded or received by the eNB. In detail, the eNBtransmits an indicator which indicates the RAP that the eNB has notsuccessfully decoded or received. Upon reception of the indicator, theUE considers the RAR reception not successful and proceeds to theselection of a random access resource although the RAR window is notended.

A UE transmits a random access preamble (RAP) to an eNB and computes theRA-RNTI based on the PRACH resource in which the RAP is transmitted(S1001). The UE starts monitoring the PDCCH for a RAR identified by theRA-RNTI within a RAR window (S1003).

The eNB receives at least one RAP from at least one UE associated withthe RA-RNTI. In this case, the eNB transmits an indicator whichindicates at least one RAP that the eNB has not successfully decoded orreceived associated with the RA-RNTI.

Preferably, the indicator indicates the concerned RAP by including: i)the RAP ID of the concerned RAP; or ii) bitmaps of RAP IDs, which is setto, e.g., “1”, for the concerned RAP.

Preferably, the indicator is identified by RA-RNTI. The indicator istransmitted via MAC signaling, where the MAC signaling can be i) MACControl Element, ii) MAC Subheader, or iii) MAC RAR.

Within the RAR window, when the UE receives an indicator identified bythe RA-RNTI which indicates at least one RAP that the eNB does notsuccessfully decoded or received (S1005), the UE considers thatreception of RAR not successful (S1007)

For example, if one of the at least one RAPs indicated by the indicationmatches to the RAP that the UE transmitted associated with the RA-RNTI,the UE considers that reception of RAR not successful, and the UE stopsfurther monitoring of the PDCCH identified by the RA-RNTI within the RARwindow (S1009). The UE proceeds to the selection of a Random AccessResource regardless of whether RAR window is ended or not, where RandomAccess Resource selection includes, e.g., selection of RAP,determination of the next available subframe containing PRACH,transmission of RAP.

Else if none of the at least one RAP IDs indicated by the indicationmatches to the RAP ID of the transmitted RAP, the UE does not stopmonitoring the PDCCH identified by the RA-RNTI within the RAR window.I.e., the UE keeps further monitoring of the PDCCH identified by theRA-RNTI within the RAR window (S1011).

FIG. 11 is a conceptual diagram for operating fast random accessprocedure in a wireless communication system according to embodiments ofthe present invention.

In case of FIG. 11, it can be applied for Machine Type communication orProSe communication to achieve power saving or latency reduction.

When a UE transmits a Random Access Preamble (RAP) including a first RAPidentifier (ID) to a peer device (S1101), the UE monitors a controlchannel for receiving an indicator including at least one RAP ID(S1103). The peer device indicates that RAP is not successfully decodedor received associated with the RA-RNTI in order not to perform needlessRA procedure. When the UE receives the indicator including at least oneRAP ID from the peer device (S1105), the UE stops monitoring the controlchannel upon reception of the indicator (S1107).

Preferably, the indicator indicates the concerned RAP by including: i)the RAP ID of the concerned RAP; or ii) bitmaps of RAP IDs, which is setto, e.g., “1”, for the concerned RAP.

Preferably, the indicator is identified by RA-RNTI. The indicator istransmitted via MAC signaling, where the MAC signaling can be i) MACControl Element, ii) MAC Subheader, or iii) MAC RAR.

When the UE receives an indicator identified by the RA-RNTI whichindicates at least one RAP that the peer device does not successfullydecoded or received, the UE considers that reception of RAR notsuccessful. At this time, the UE stops monitoring the control channelupon reception of the indicator.

Else if none of the at least one RAP IDs indicated by the indicationmatches to the RAP ID of the transmitted RAP, the UE does not stopmonitoring the control channel identified by the RA-RNTI (S1109). I.e.,the UE keeps further monitoring of the control channel identified by theRA-RNTI within the RAR window.

FIG. 12 is an example scenario for operating fast random accessprocedure in a wireless communication system according to embodiments ofthe present invention.

The UE transmits a RAP with RAP ID=7 and computes RA-RNTI (S1201). TheUE shall monitor the PDCCH for RAR(s) identified by the RA-RNTI withinthe RAR window which starts at the subframe that contains the end of theRAP transmission plus three subframes (S1203).

Within the RAR window, the UE receives an Indication via MAC signalwhich indicates the RAP that the eNB has not successfully decoded orreceived. The UE checks whether RAPID=7 is indicated in the receivedIndication.

As RAPID=7 is not indicated in the received Indication, the UE keepsmonitoring the PDCCH for RAR (S1205).

Meanwhile, as RAPID=7 is indicated in the received Indication, the UEconsiders that reception of RAR not successful and stops monitoring thePDCCH for RAR (S1207).

Further, the UE proceeds to Random Access Resource selection. The UEdetermines the next available subframe containing PRACH and transmitsthe RAP even within the RAR window. And then, the UE transmits the RAPeven though the RAR window is not ended (S1209).

FIGS. 13A to 13D are diagrams for a new MAC PDU according to embodimentsof the present invention.

The indicator includes at least one of RAP ID so that the indicatorindicates at least one RAP that the eNB has not successfully decoded orreceived associated with the RA-RNTI.

The indicator indicates the concerned RAP by including: i) the RAP ID ofthe concerned RAP (FIG. 13A); or ii) bitmaps of RAP IDs, which is setto, e.g., “1”, for the concerned RAP (FIG. 13C).

FIG. 13A is a RAPID MAC CE including only one RAP ID and FIG. 13B is anexample of MAC PDU consisting of a MAC header, RAPID MAC CEs, and MACRARs. In RAPID MAC CE of FIG. 13A, only one of the concerned RAP isindicated by including the corresponding RAP ID. An LCID is allocatedfor this RAPID MAC CE. By using the above RAPID MAC CE, an example ofMAC PDU addressed by a RA-RNTI containing MAC header, RAP ID MAC CEs,and MAC RARs are shown as FIG. 13B.

FIG. 13C is a RAPID MAC CE including multiple RAPs by using bitmap, andFIG. 13D is an example of MAC PDU consisting of a MAC header, RAPID MACCE, and MAC RARs.

In RAPID MAC CE of FIG. 13C, multiple concerned RAPs are indicated byincluding the corresponding RAP IDs. For example, Li field is set to 1for the concerned RAP with RAP ID=i. An LCID is allocated for this RAPIDMAC CE.

By using the above RAP ID MAC CE, an example of MAC PDU addressed by aRA-RNTI containing MAC header, RAP ID MAC CEs, and MAC RARs are shown asFIG. 13D.

In summary, a conventional RA procedure considers that the Random AccessResponse reception is not successful if no Random Access Response isreceived within the RA Response window or if none of all received RandomAccess Responses contains a Random Access Preamble identifiercorresponding to the transmitted Random Access Preamble.

However, according to this invention, if RAP identifier corresponding tothe transmitted Random Access Preamble is indicated as not received bythe eNB, the UE considers the Random Access Response reception isconsidered not successful, additionally.

By that unnecessary RAR reception procedures can be terminated early, itcan get the effect of power saving and latency reduction. That is, ifthe UE can be sure that the RAR is not transmitted in the RAR window,the UE can stop unnecessary PDCCH monitoring early, and the UE canselect and transmit a new RAP. This enables an efficient RA procedure.

The embodiments of the present invention described hereinbelow arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It is obvious tothose skilled in the art that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

In the embodiments of the present invention, a specific operationdescribed as performed by the BS may be performed by an upper node ofthe BS. Namely, it is apparent that, in a network comprised of aplurality of network nodes including a BS, various operations performedfor communication with an MS may be performed by the BS, or networknodes other than the BS. The term ‘eNB’ may be replaced with the term‘fixed station’, ‘Node B’, ‘Base Station (BS)’, ‘access point’, etc.

The above-described embodiments may be implemented by various means, forexample, by hardware, firmware, software, or a combination thereof.

In a hardware configuration, the method according to the embodiments ofthe present invention may be implemented by one or more ApplicationSpecific Integrated Circuits (ASICs), Digital Signal Processors (DSPs),Digital Signal Processing Devices (DSPDs), Programmable Logic Devices(PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers,microcontrollers, or microprocessors.

In a firmware or software configuration, the method according to theembodiments of the present invention may be implemented in the form ofmodules, procedures, functions, etc. performing the above-describedfunctions or operations. Software code may be stored in a memory unitand executed by a processor. The memory unit may be located at theinterior or exterior of the processor and may transmit and receive datato and from the processor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from essential characteristics of the presentinvention. The above embodiments are therefore to be construed in allaspects as illustrative and not restrictive. The scope of the inventionshould be determined by the appended claims, not by the abovedescription, and all changes coming within the meaning of the appendedclaims are intended to be embraced therein.

INDUSTRIAL APPLICABILITY

While the above-described method has been described centering on anexample applied to the 3GPP LTE system, the present invention isapplicable to a variety of wireless communication systems in addition tothe 3GPP LTE system.

The invention claimed is:
 1. A method for a User Equipment (UE)operating in a wireless communication system, the method comprising:transmitting a Random Access Preamble (RAP) including a first RAPidentifier (ID) to an e-NodeB (eNB); starting monitoring of a PhysicalDownlink Control Channel (PDCCH) addressed by a Random Access-RadioNetwork Temporary identifier (RA-RNTI) during a Random Access Response(RAR) window; receiving, from the eNB, an indicator including at leastone RAP ID, wherein one of the at least one RAP ID matches the first RAPID, and wherein the indicator informs the UE that the RAP was notsuccessfully decoded or received by the eNB; and stopping monitoring ofthe PDCCH addressed by the RA-RNTI upon receiving the indicator beforean end of the RAR window, wherein the indicator is received using a MACPDU, wherein the MAC PDU contains a MAC header and a RAP ID MAC CEincluding a bitmap, and wherein a field in the bitmap indicates thefirst RAP ID.
 2. The method according to claim 1, wherein the indicatoris received using the RA-RNTI.
 3. The method according to claim 1,wherein the indicator is received using a Medium Access Control (MAC)Protocol Data Unit (PDU), wherein the MAC PDU contains a MAC header andat least one RAP ID MAC Control Element (CE), and wherein one of the atleast one RAP ID MAC CE includes the first RAP ID.
 4. The methodaccording to claim 1, further comprising: determining that an RARreception is unsuccessful upon reception of the indicator.
 5. The methodaccording to claim 4, further comprising: selecting a new Random AccessResource upon receiving the indicator.
 6. The method according to claim5, wherein selecting the new Random Access Resource includes selecting anew RAP, determining the next available subframe containing a PhysicalRandom Access Channel (PRACH), or transmitting the new RAP.
 7. Themethod according to claim 1, wherein when none of the at least one RAPIDs indicated by the indicator matches the first RAP ID, the UEcontinues monitoring of the PDCCH identified by the RA-RNTI within theRAR window.
 8. The method according to claim 1, wherein the RAR windowstarts at a subframe that contains end of the RAP transmission plusthree subframes.
 9. A method for a User Equipment (UE) operating in awireless communication system, the method comprising: transmitting aRandom Access Preamble (RAP) including a first RAP identifier (ID) to apeer device; monitoring a control channel for receiving an indicatorincluding at least one RAP ID; receiving, from the peer device, theindicator including at least one RAP ID, wherein one of the at least oneRAP ID matches the first RAP ID, and wherein the indicator informs theUE that the RAP was not successfully decoded or received by an e-NodeB(eNB); and stopping monitoring of the control channel upon receiving theindicator before an end of a Random Access Response (RAR) window,wherein the indicator is received using a MAC PDU, wherein the MAC PDUcontains a MAC header and a RAP ID MAC CE including a bitmap, andwherein a field in the bitmap indicates the first RAP ID.
 10. The methodaccording to claim 9, wherein the UE monitors the control channel duringthe RAR window.
 11. A User Equipment (UE) operating in a wirelesscommunication system, the UE comprising: a receiver and transmitter; anda processor, operatively coupled to the receiver and transmitter,wherein the processor is configured to: control the transmitter totransmit a Random Access Preamble (RAP) including a first RAP identifier(ID) to an e-NodeB (eNB); start monitoring of a Physical DownlinkControl Channel (PDCCH) addressed by a Random Access-Radio NetworkTemporary identifier (RA-RNTI) during a Random Access Response (RAR)window; control the receiver to receive, from the eNB, an indicatorincluding at least one RAP ID, wherein one of the at least one RAP IDmatches the first RAP ID, and wherein the indicator informs the UE thatthe RAP was not successfully decoded or received by the eNB; and stopmonitoring of the PDCCH addressed by the RA-RNTI upon receiving theindicator before an end of the RAR window, wherein the indicator isreceived using a MAC PDU, wherein the MAC PDU contains a MAC header anda RAP ID MAC CE including a bitmap, and wherein a field in the bitmapindicates the first RAP ID.